Burj Khalifa, The Shard, and Rivals by Eva Bogomil Introduction From the early days, we have invariably been interested in the world we live in, exploring, analysing, and altering it at our will. Humanity has gone a long way from caves to modern skyscrapers, aiming for ever greater heights. The power of human ingenuity has conquered the elements to reach the sky and beyond. Nowadays technologies allow us to build skyscrapers that totally change our idea of a modern world. Throughout the centuries brilliant engineers have been inventing more advanced and complex technologies, expanding our abilities. The Acropolis, St Paul’s Cathedral, the Eiffel Tower and the Sydney Opera House are all marvellous buildings that have remained objects of admiration for historians, architects, and artists, as well as a source of inspiration for many generations. Even to the general public the structures appear breathtaking. The 21st century saw the dawn of super-skyscraper construction. The Shard, Taipei 101, the Princess Tower, the Abraj Al-Bait Towers, and the Shanghai Tower are just some of the outstanding examples the modern world can be proud of. Burj Khalifa, currently the tallest building in the world, crowns this list of our achievements (Figure 1.0) which keep attracting people, making them wonder how such structures could have been built. Figure 1.0: Height comparison of some of the tallest buildings in the world This essay will focus mainly on London’s Shard and Dubai’s Burj Khalifa. Both of these skyscrapers are unique in their own way, yet similar. The Shard — currently the tallest building in the United Kingdom — dominates London skyline. One cannot ignore this magnificent building, yet Burj Khalifa, currently the tallest building in the world, interests me the most since its construction was a definitive breakthrough in the history of skyscrapers. The skills and technology had to be taken to a completely new level. The very construction of both skyscrapers challenged the forces of nature. Overview The Shard. The magnificent shiny 95-storey-high skyscraper became the tallest building in Europe upon its completion on 30 March 2012 at a height of 309.6 metres (1,016 feet). The project was first envisaged in 2000, but it was not until 19 March 2009 that the works had started. The delay was caused by the Chartered Association of Building Engineers (CABE) and English Heritage who believed that the construction of such a skyscraper would ruin the view onto such historic London places as St Paul’s Cathedral and Westminster (Figure 2.1). ‘Tear through historic London like a shard of glass’, said English "1 Heritage, unintentionally giving the skyscraper its current name [12]. That happened despite the Shard’s designer, Renzo Piano, claiming to have been inspired by the spires of London churches and masts of tall ships [4]. Burj Khalifa. The tallest skyscraper in the world with 160 floors and 828 meters high, located in Dubai, UAE was launched on 4 January 2010 (Figure 2.2). The tower is classified as ‘supertall’ (with a height in excess of 1,000 feet) [3]. After 6 years of combined effort of more than 12,000 workers, the tower Figure 2.1: The ‘view’ planning of the Shard has become the icon of the city. The Image: http://www.shardldn.com/construction-history-html/ design of Burj Khalifa was inspired by local nature — the spider lily. The building also set a number of World Records, including the highest occupied floor, the tallest operational elevator, and the tallest aluminium and glass façade, among others [3]. Foundations The Shard towers above Southwark just a couple of streets away from the river Thames. The hole for its foundation was dug down to the clay layer. To construct a firm foundation for the skyscraper and prevent the structure from sinking into the clay, the latter was removed before filling the concrete [2]. The Shard was planned on the site of the former Southwark Towers, and its piles remained in the ground. Since it was impossible to remove them and because the area was surrounded by the London Bridge Station and other facilities, the engineers had to come up with an alternative way to construct the basement [13]. In order to reduce the cost and the timescale, the top-down construction method was used. It enabled the first three storeys and the underground structure to be built simultaneously: the secant pile wall was built together with the steel columns of the bearing piles. The giant hole in the ground level slab gave access to the piles, while the wall kept them from being flooded. A rig attached to the steel plunge columns was then used for supporting the concrete core, while the excavation of the basement floors was taking place underneath. By the time the thin basement slab had been completed, the Shard already had 20 storeys [1][13][14]. This was, indeed, a truly innovative method Figure 2.2: Burj Khalifa (Figure 3.1). Image: https://www.archdaily.com/882100/burj-khalifa-som "2 Miles away from the Shard, Burj Khalifa is situated in the desert of Dubai. Yet it faced similar problems. Weak and fractured rock, saturated with ground waters was a challenge for the engineers. It could not carry much weight, and to prevent t h e b u i l d i n g f r o m sinking into the sand, 125 piles were made Figure 3.1: The foundation of the Shard out of steel-reinforced Image: http://www.engineersjournal.ie/2016/01/26/engineering-the-shard/ concrete [8]. In order to build a foundation that could support the structure, 50-meter-deep bore holes were dug in the soil and filled with viscous polymer slurry to stop them from caving in. Concrete was then poured in, displacing the lower density slurry and forming foundation piles. High sulphate- rich ground waters posed the danger of corrosion. To minimise potential damage special corrosion inhibitors were added to the concrete [8]. Structure The amazing thing about the construction of the 95 storeys of the Shard and the 160 storeys of Burj Khalifa is that the work was completed in 4 and 6 years, respectively. In construction business, time is money, making the timescale one of the main priorities. A major development in the skyscraper technology took place during the construction of the World Trade Centre in New York City in 1975, when the so- called «kangaroo» cranes were used to deliver pre-fabricated skeleton blocks to the upper floors. Every time each subsequent storey was built, the cranes lifted themselves up the building [8]. Figure 3.2: Foundation diagram of Burj Khalifa The same type of cranes was used in the showing the areas of different load (red for highest, construction of Burj Khalifa. Steel skeleton blue for lowest) parts were made on the ground and lifted Image: https://commons.wikimedia.org/wiki/ File:Burj_Khalifa_foundation_structure.gif up. The resultant shape was then filled with concrete. After it solidified, the shape could «jump up» to the next floor [3][8]. This enabled the workers to complete a storey almost every tree days. Once the building reached its 99th and 159th floors, special ‘recovery’ cranes were used to disassemble the operating cranes. The cranes at the very top, however, did that themselves when moving down level by level [3]. With the Shard, an even more exciting method was developed. A whole floor shape was moved up the building and filled with concrete, so that the core grew up at a rate of 3 meters a day (Figure 4.1) [2]. "3 At greater heights, it becomes progressively harder to bring the concrete up. This was a serious issue when constructing Burj Khalifa. The process was done only at nighttime. Concrete was cooled down and water was replaced with ice. It was a real challenge for the chemists to get the right consistency of the concrete: not thin, yet not too thick, otherwise there was a risk of it hardening inside the tubes. Four different types of concrete mixes were used at different heights [8]. It took longer than 40 minutes to pump up the concrete to the top floors at a pressure of over 80 MPa [3]. Along its length, the pipe had several 180 degree bends to imitate the loss of pressure [15]. Consequently, Burj Khalifa broke the world record for vertical concrete pumping [3]. Figure 4.1: The view on the core construction of the The mixed-use purpose of the Shard led Shard. The concrete mould is moved up for each to the unusual application of the materials level. Image: http://sbi.se/uploads/source/files/SBD/presentationer-12/1530.pdf (Figure 5.1). As the offices needed large open space, those floors were constructed from steel which behaves equally well in both tension and compression. All of the equipment, such as air conditioning and power cables, was hidden between the ceiling and the slab, using I-beams. At the same time, hotel and residential floors had to be sub- divided into smaller rooms, and it was decided to use concrete, because concrete columns could be hidden in the walls, and concrete slabs are thinner so more floors could be built. Moreover, concrete is very sound absorbing, which was a great advantage for the residential space [1]. A buttressed-core system was used in the construction of Burj Khalifa (Figure 5.2) [15]. Its core has a hexagon shape with three wings anchored to it. It makes each wing to be supported by the other two. This system allows us to construct much higher buildings than ever before, and was first tried out on the Tower Palace, Seoul [7][8].